Analytical methods for the qualitative and quantitative determination of lithium ion (Li.sup.+) are of interest in establishing the levels of therapeutic lithium in humans when lithium-type medications are administered as therapy to overcome manic depressive states in human beings. Such methods require that the lithium be determined in the presence of sodium ion.
A U.S.S.R. Author Certificate No. SU1057500A discloses a material having the formula ##STR2## as a chromogenic agent for lithium determination. However, following the instructions of the Author Certificate we have been unable to make this compound. Moreover, the same Author Certificate appears to state that compounds of the formula ##STR3## where X=--, --CH.sub.2 --, --CH.sub.2 OCH.sub.2 --, --CH.sub.2 OCH.sub.2 CH.sub.2 OCH.sub.2 --;
R=--H, CN, --COCH.sub.2 ; PA0 R.sub.1 =--H, --NO.sub.2. PA0 Y represents --CH.sub.2 CH.sub.2 --, --CH.sub.2 CH.sub.2 CH.sub.2 -- or --CH.sub.2 CH.sub.2 --O--CH.sub.2 CH.sub.2 --; and PA0 R.sub.1, R.sub.2, R.sub.3 and R.sub.4 each independently represent alkyl having up to 12 carbon atoms, halogen (e.g. Cl.sup.-, B.sub.r.sup.-, I.sup.-), alkoxy having up to 12 carbon atoms or NO.sub.2.
are impossible to use as microbiological color reagents. Biological fluids such as blood serum contain concentrations up to 150 milliMolar (mM) of sodium. Presently there are no reagents with which Li.sup.+ can be correctly determined in the presence of sodium.